It’s not often that the word kill moves us to buy something. Except when it comes to weeds. We want our weeds gone, not wounded, not rendered sickly, but dead. So much so that we may be tempted to reach for a bottle that boasts the promise killer. Even if a pair of gardening gloves and a sturdy hoe are our weapons of choice instead of chemical warfare, any gardener worth her seed knows the survival of wanted plants depends on destroying that which is unwanted, the weeds that persistently threaten to rule.   Weeds must be killed. Otherwise, they’ll kill. This past spring, I planted my first rose bush.…